Gingival matrix proteins are being investigated in our laboratory to establish base line information on the nature of the alterations accompanying inflammatory processes, thereby defining the role of the intercellular macromolecules in periodontal disease. Detailed structural studies at the molecular level of the collagenous and noncollagenous components of gingiva from normal and diseased tissues are in progress to establish the biochemical nature of these components and their physiological role in the maintenance of gingival tissue. Heterogeneity of gingival collagen has been established in the present phase of the project, type I being the major component. The ratio of types III/I decreases in chronic periodontitis gingiva. We have recently described type V collagen in bovine gingiva and we here report on the same collagen type in chronically inflamed human gingiva. In this tissue the per cent of type V collagen was higher than in the bovine tissue. The possible role of this collagen type in periodontal disease will be examined. It is now essential to characterize other collagenous chains and to determine their significance for normal gingival tissue function. Our data suggested that the noncollagenous moiety which appeared be firmly associated with the collagenous component, possibly convalently, showed significant quantitative and qualitative changes in the diseased tissue. A correlation of the structural alterations in gingival connective tissue macromolecules with histological and clinical manifestations of periodontal disease will provide more information on the molecular basis and etiology of the disease.